In communication applications, high-density packaging is an important issue. This is true whether the communications are based upon transmissions of electrical signals or optical signals. A related consideration is the cost of fabrication. The density of fiber optic modules that can be positioned along a printed circuit board (PCB) of a fiber optic-based Local Area Network (LAN) hub or similar system significantly impacts the per channel cost of the system.
Small-form fiber optic modules allow a high density of transmit and receive channels. Such modules include fiber optic transceivers which enable a light source to be coupled to a transmit fiber and allow a detector to be coupled to a receive fiber. FIG. 1 illustrates one known arrangement for coupling optical fibers 10 and 12 to a pair of solid state device packages 14 and 16 that are secured to a PCB, not shown. The optical fibers are embedded within a connector 18. For a standardized MT-RJ fiber pair, the center-to-center distance of the two fibers is 0.75 mm. For example, the connector may be a Mini-Mechanically-transferrable Push-On (Mini-MPO) connector type. Typically, the density of the transmitter and receiver channels is determined by the size requirements of the device packages. The solid state devices must be packaged to provide both optical and electrical isolation of the transmit and receive signals, as well as environmental protection. In the example shown in FIG. 1, the packages of the devices are shown as conventional Transistor Outline (TO) style cans. Each of the cans includes a pair of leads 20 and 22 that are soldered to the printed circuit board, which includes the drive and processing electronics for a transmitter chip 24 and a detector chip 26. The transmitter chip may be a light emitting diode (LED) or a laser diode. The detector chip 26 may be a photodiode.
The TO cans 14 and 16 of FIG. 1 are positioned such that when the connector 18 is inserted into a female connector seated on the same PCB as the TO cans, the exchange of optical signals is along a single plane. With regard to the transmit channel, the transmitter chip 24 generates an optical signal that is directed to a lens 28 of the TO can 14. The can lens 28 is cooperative with a collimating lens 30 to produce a collimated beam that impinges the mirror 32. The first mirror redirects the light path to a second mirror 34, which again redirects the light path for alignment with the transmit fiber 10. A lens 36 focuses the signal onto the aligned fiber 10.
The receive channel follows a path similar to the transmit channel, but in the opposite direction. Light from the fiber 12 is collimated by a lens 38 and impinges a third mirror 40. The redirected optical signal is again redirected by a fourth mirror 42. The optical signal is then operated upon by a lens 44 and a can lens 46 to focus the received signals onto the detector chip 26.
The arrangement of FIG. 1 provides beam translation along two axes, i.e., the X axis and the Z axis indicated in FIG. 1. This allows the spacing between the two channels to be increased from the 0.75 mm spacing of the connector 18 to a greater spacing between the two TO cans 14 and 16, e.g., a spacing of 6.2 mm.
Other optical couplers for connecting optical fibers to TO cans are known. U.S. Pat. No. 4,701,010 to Roberts describes a molded body having reflecting surfaces for connecting a fiber to a detector TO package or an emitter TO package. A slot extends into the body to allow insertion of a filter, such as a dichroic mirror, or a beam splitter, depending upon the desired application.
While the prior art systems operate well for their intended purposes, what is needed is a system that provides further reductions in the fabrication cost, without a sacrifice in optical performance.